An internal combustion engine is known to comprise valves, at least one per cylinder, for the admission or the exhaust of gases. These valves are controlled synchronously with the operation of the engine. Their opening or closing time must be controlled very accurately.
Until now, the opening or closing of valves has been carried out mainly mechanically. However, an electromechanical type valve opening or closing control has been proposed for the past few years, which makes it possible to simplify the embodiment of the engine and the supplementary engine control functions because the valves can be controlled at will thanks to electronic control means independently from the structure of the engine.
These electromechanical valve opening and closing control devices comprise a magnetic blade or plate cooperating with one or two electromagnets and springs. The blade moves between the two electromagnets. One end of the course of the blade corresponds to the closed position of the valve and the other end of the course corresponds to the open position. In each end position, one spring is compressed and another spring is relaxed. The electromagnet is used to maintain the blade in each end position while the springs help to displace the blade from one end of its course to the other.
A particularly simple type of actuating device was described in European Patent No. 1 174 596. This device is shown in FIG. 1. A single electromagnet 1, inside of which a permanent magnet 5 is arranged, is provided in this known embodiment. The magnetic circuit of the electromagnet comprises, in a sectional view, symmetrically in relation to the axis of a rod 16, on the one hand, two branches 8 and 9, with the ends of which a magnetic blade 15 comes into contact in the closed position of the valve 17, and, on the other hand, the branches 10 and 11, at the ends of which the blade is supported in the open position of the valve.
The magnetic induction created by the permanent magnet 5 maintains the blade 15 in each of the end positions, either at the end of the branches 8 and 9 or at the ends of the branches 10 and 11.
To pass over from one position into the other, a coil 2 wound around a branch of the magnetic circuit is supplied in such a way as to generate a magnetic field that opposes the effect of the magnet. Under these conditions, the compressed spring pushes the blade 15 toward the other end position. In the position shown in FIG. 1, the compressed spring 18 pushes the blade 15 toward the ends of the branches 10 and 11.
The structure of this actuating device is particularly simple and the electric energy consumption is low. However, this structure has a space requirement that is hardly compatible with the compactness desired for the embodiment of engines. Moreover, start-up is difficult from the mid-course position, which corresponds to the equilibrium position of the springs.